Method of vacuum slag refining of metal in the course of continuous casting



y 7, 1970 v. G. VOSKOBOINIKOV ET AL 3,5

METHOD OF VACUUM SLAG REFINING OF METAL IN THE COURSE OF CONTINUOUSCASTING Filed July 12 1967 United States Patent 3,519,059 METHOD OFVACUUM SLAG REFINING 0F METAL IN THE COURSE OF CONTINUOUS CASTING ViktorGrigorievich Voskoboinikov, Ulitsa 1812 goda, kv. 18, dom 7; OlegVyacheslavovich Kurnushko, Zelenograd, korpus 214, kv. 72; VladislavSemenovich Koziakov, Universitetslry prospekt 23, korpus 2, kv. 28; andAnatoly Fedorovich Kablukovsky, Ulitsa Usievicha 29, korpus 2, kv. 57,all of Moscow, U.S.S.R.; Aron Yakovlevich Tseitlin, Prospekt Lenina 63,kv. 100, Tula, U.S.S.R.; Viktor Savelievich Rutes, 7 Parkovaya ulitsa15, kv. 12; and Anatoly Georgievicll Shalimov, 3 Parkovaya ulitsa 50,korpus 3, kv. 30, both of Moscow, U.S.S.R.; Vladimir AndreevichKazansky, Ulitsa Anosova 3, kv. 4, Tula, U.S.S.R.; Jury Evgenievich Kan,Bolshaya Kolkhoznaya ploschad 14/7, kv. 22, Moscow, U.S.S.R.; VasilyNikolaevich Ustjuzhanin, Ulitsa Anosova 8/16, kv. 12, Tula, U.S.S.R.;and Anatoly Alexeevich Markin, Ulitsa Burdeuko ll-a, kv. 9, Moscow,U.S.S.R.

Filed July 12, 1967, Ser. No. 652,883 Int. Cl. B22d 11/10 U.S. Cl. 16453Claims ABSTRACT OF THE DISCLOSURE In the casting operation of a metal oralloy, a vacuum is applied to a stream of the metal which is broken upinto streams of metal drops by gases released from the metal, the metaldrops passing through a layer of synthetic slag located in a vacuumchamber which is above the mold. The metal is purified from sulphur,nonmetallic inclusions and residual gases and passes into the moldwherefrom a continuous ingot is removed.

The present invention relates to the field of casting metals and alloys.

Known in the prior art is a method and device for easting liquid metal,wherein the liquid metal is supplied from a ladle into a vacuum chamber,itself in the form of a ladle, where there are effected the operationsof separating the stream of liquid metal, deoxidizing and al loying it.Then the metal is tapped into the principal casting arrangement,disposed under the chamber.

Metal is supplied into a water-cooled mold through a special holeprovided in the lower part of the arrangement.

The whole system, comprising all the equipment ranging from the ladle tothe casting arrangement, is hermetrically sealed. When the liquid metalis in the casting arrangement, an inert medium is to be maintained aboveit (see, for example, the US. Pat. No. 3,125,440, according to the Class75-49).

The use of a vacuum in the casting of metal in an inert medium does notprevent the formation of a floating crust in the mold. There ispreserved a nonuniformity of solidification and non-metallic inclusionsare formed. The existing method does not prevent the formation of hotlongitudinal cracks caused by a retarded shrinkage of the metal skin,the nonuniform solidification along the width of faces and thedevelopment of thermal stresses. This method of casting is likely toproduce circulation currents in the mold, slowing down the process ofsolidification and the obtention of a cast billet which is unifiedshell.

Additionally, the nonuniform solidification considerably increases theextent of dendritic segregation in the direction towards the ingotcenter, which is likely to interfere with the achievement of maximumspeeds of solidification and the obtention of a cast billet which isuniform with regard to the content of alloying elements.

An object of the present invention is to provide such a method ofcasting metals and alloys in a mold, and a device for effecting same,which ensures the heating of the meniscus of the metal in a closed andhermetically sealed system, comprising a heating chamber with slag and amold.

Another object of the present invention is to provide such a method ofcasting metals and alloys in a mold, and a device for eifecting same,which ensures the creation of a uniform solidification front.

A further object of the present invention is to provide such a methodand device for casting metals and alloys which enables the cleaning ofthe metals and alloys from harmful impurities and nonmetallicinclusions.

In conformity with the above and other objects, the method of castingmetals and alloys in a mold, in which the stream of metal or alloy beingcast is broken up into streams of metal drops, contemplates, accordingto the invention, that the streams of metal drops thus formed are passedthrough a layer of a fluid refining slag and the liquid metal is thusstored under the layer of slag above the mold level with the subsequentforming of an ingot therefrom in the mold.

It is expedient that the temperature of the layer of the fluid refiningslag be maintained below that of the liquid metal or alloy being cast,and above the temperature of the accumulated liquid metal to be refined.

In the process of casting, the heating of the fluid refining slag,liquid metal or alloy to be refined over the mold and in the upperportion of the mold may be effected by utilizing to an electromagneticfield.

The method provides for deoxidizing and alloying the liquid metal oralloy to be cast in the process of casting thereof under a layer of slagover the mold, as Well as for the renewal of the slag above the mold.

In the device for effecting the method, there is provided a ladlecomplete with a mold and a vacuum chamber disposed therebetween, saidchamber being intended for degassing the metal or alloy to be cast, thevacuum chamber, according to the invention, being made so as to beheated, and being provided with a hermetic channel and a batcher forfeeding therein the refining slag, which is retained by the metal storedin the chamber. The internal walls of the chamber in the upper and lowerportions thereof are made of a heat-insulating material; in their lowerpart they are made in the form of the upper section of the mold. Theinternal wall of the median portion of the chamber are made of anelectrically conducting material.

The chamber may be heated by the aid of an inductor, disposed on theperiphery of the chamber and thermally insulated from its internalWalls.

The inductor is assembled of separate sections so as to enablecontrolling the temperature throughout the height of the chamber and inthe area of its junction with the mold.

The chamber is provided with a heated channel in tended for the removalof slag, said channel being disposed above the area of the junction ofthe chamber with the mold above the level of the liquid metal stored,and a hermetical slag collector provided with an exchangeable slag pot.

The chamber may be equipped with a pickup for indicating the level ofthe accumulated liquid metal and a pickup for indicating the level ofthe refining slag over the liquid metal stored.

The nature of the present invention will further be made more fullyapparent from a consideration of the following description of anexemplary embodiment thereof, taken in conjunction with the drawing, thesole figure of which is a diagrammatic view, partly in section of adevice for effecting the method of casting metals or alloys according tothe invention.

In conformity with the proposed method, the stream of molten metal,introduced into a chamber under a vacuum, is degassed to a considerableextent and broken up into streams of metal drops. The streams of metaldrops thus formed pass through a layer of the fluid refining slag, whichresults in cleaning the metal from harmful impurities and nonmetallicinclusions, the metal thus cleaned being stored under the slag.

To ensure a more uniform solidification front and enable an interactionbetween the metal and slag in the process of casting, the level ofliquid metal is brought out from the mold into the chamber.

The fact that the fluid slag is present on the heated meniscus of metalabove the level of the mold is likely to preclude the formation of thefloating crust and prevent the slag from getting into the mold.

In order to provide conditions for a directed heat exchange between theliquid metal and mold, the temperature of the fluid refining slag is tobe maintained below the temperature of the metal being cast and abovethat of the liquid metal being stored. Under these conditions, theaccumulated liquid metal is directly formed into an ingot in the mold.

The device for effecting the method comprises a ladle 1 with a liquidmetal and a batcher 2 for slag, both mounted on a working platformdisposed above a heated vacuum chamber 3.

The internal walls of the chamber 3 in the upper and lower portionsthereof are made of a heat-insulating material, and in the lower partthey are made in the form of the upper section of the mold 4. Such ashape of the lower part of the chamber 3 is adapted to facilitate theheating of the metal introduced therein which excludes the probabilityof its scaffolding in the area of junction of the chamber 3 with themold 4. The internal walls of the chamber in its median part are made ofan electrically conducting material.

The chamber is heated by an inductor 5, assembled of separate sections,disposed on the periphery of the chamber 3 and thermally insulated fromits internal walls.

The heating of slag in the chamber is effected through internal,electrically conducting walls of the chamber by eddy currents.

From the batcher 2 the refining slag is supplied through a hermeticchannel 6 into the chamber, the slag being retained there by the liquidmetal stored in the chamber. The used slag is tapped through a heatedchannel 7 into a slag collector 8 connected to the heated chamber 3.

In the casting process, deoxidizers and alloying additives are alsointroduced through the hermetic channel 6 into the chamber 3. Theinteraction of the deoxidizers with metal occurs both in the slag and inthe liquid metal in the chamber.

Oxides resulting from the deoxidation of metal are removed into theheated slag, which prevents the formation of a floating crust andsurface defects in the ingot.

In the beginning of the casting process, a dummy bar is placed in theupper part of the mold 4 below the chamber. The pickup 9 indicating thelevel of metal in the chamber (which is conventionally shown in thedrawing) sends a signal to the block 10 for controlling the supply ofmetal, which signal causes the stopper of the ladle to rise through adrive 11. The metal fills the upper 4 part of the mold 5 and the lowerportion of the chamber 3 up to the specified level.

The liquid metal brought into the chamber 3 serves as a hydraulic seal,and provides for maintaining the desired vacuum in the space above theslag.

The same volume of liquid metal prevents the metal from getting into themold.

The fact that the level of metal is maintained in the heated chamber 3above the mold under conditions in which the level varies in the castingprocess, is likely to facilitate the process of automatic control of theliquid metal feed from the ladle into the chamber, and then into themold, not affecting thereby upon the established conditions of heattransfer between the liquid metal and mold.

After the chamber 3 has been filled with liquid metal, the block 10 forcontrolling the feed of metal actuates a speed presetting device 12,which is intended to maintain the speed of the ingot withdrawal by theaid of a drive 13. Simultaneously, the optimum speed of supplying liquidmetal into the chamber 3 is automatically established by a signal of theblock 10 for feeding metal into the chamber, the optimum speed beingadopted in such a manner as to allow the level of liquid metal to varyonly in the prescribed range.

When the lower part of the chamber 3 is filled with liquid'metal up tothe specified level, prescribed by the block 10 for controlling the feedof metal, there are automatically actuated the systems for creating avacuum and supplying slag into the chamber on the liquid metal. As soonas the required height of the slag is achieved, a pickup 14, whichindicates the level of slag, generates a signal to actuate, through ablock 15 which controls the slag supply and a drive 16, the batcher 2for feeding the slag.

When the median part of the chamber 3 is being filled with slag, thelatter begins to flow out through the heated channel 7 into the slagcollector 8 under a pressure equal to that present in the heatedchamber.

If the pickup 9, indicating the level of metal in the heated chamber 3,sends a signal indicative of a deviation of the separation boundarymetal-slag, i.e., the speed of supplying liquid metal from the ladleinto the chamber proves to be faster or slower than the speed of theingot withdrawal, established by the presetting device, then the block10 for controlling the supply of liquid metal into the chamber will vary(through the drive 11 by the aid of the ladle stopper) the feed of metalin such a manner that the separation boundary metal-slag returns to thespecified level.

In a similar manner, when the position of the boundary slag-gas varies,a signal is emitted by the pickup 14 and the boundary is established ata certain level by the batcher 2.

After the metal is no longer fed into the heated chamber in the positionstopper closed in ladle 1, the separation boundary of metal and slag,fixed by the pickup 9, is lowered to the adopted value. Then the block10 for controlling the supply of metal into the heated chamberdisconnects the presetting device 12 and stops the batcher 2.

The remaining refining slag flows from the heated chamber into the slagpot 8, upon which the ingot remaining in the mold is to be extracted.

What is claimed is:

1. A method of continuous casting of metals, said method comprisingdischarging a stream of metal being cast into a vacuum chamber where thestream is broken up into streams of liquid, metal drops, then passingthe streams of metal drops thus formed through a layer of a fluidrefining slag introduced into said chamber so as to remove harmfulimpurities and nonmetallic inclusions therefrom, accumulating the liquidmetal under the slag above the level of a mold and continuouslywithdrawing an ingot from the mold wherein the metal is formed.

2. A method according to claim 1, wherein the temperature of the layerof the fluid refining slag in the vacuum chamber is maintained below thetemperature of the metal being cast and above that of the refined,liquid metal accumulated in the mold.

3. A method according to claim 1, wherein in the process of vacuum slagrefining and casting of metal, the fluid refining slag above the mold inthe vacuum chamber and the metal in the upper part of the mold areheated by an electromagnetic field.

4. A method according to claim 1, wherein the metal is deoxidized andalloyed in the vacuum chamber under the layer of slag and above themold.

5. A method according to claim 1 comprising changing the refining slagabove the mold as the metal is being removed from the vacuum chamber.

References Cited 10 J. SPENCER OVERHOLSER, Primary Examiner R. S.ANNEAR, Assistant Examiner U.S. Cl. X.R.

